This invention relates to an improved process for producing alkyltetrahydroanthrahydroquinones in solvent systems suitable for the production of hydrogen peroxide, in which solutions of alkyl- 5,6,7,8-tetrahydroanthrahydroquinones are obtained which can be used directly as working solutions for the production of hydrogen peroxide, or from which alkyltetrahydroanthrahydroquinones or, following their oxidation with an oxygen-containing gas, the corresponding alkyltetrahydroanthraquinones can be isolated, if desired.
In the production of hydrogen peroxide by the anthraquinone process (AO process), alkylanthraquinones dissolved in suitable solvents are used as reaction carriers. These solutions of alkylanthraquinones are referred to as working solutions. It is also known that alkylanthraquinones in admixture with hydrogenation resistant alkyl-5,6,7,8-tetrahydroanthraquinones can be used in the working solution for the production of hydrogen peroxide by the anthraquinone process. The tetrahydroanthraquinones are formed spontaneously in succession during the process cycle as hydrogenation by-products of the alkylanthraquinones in the working solution. In order to be able to make better use of the advantages of alkyltetrahydroanthraquinones in the production of hydrogen peroxide, it is known in the art to produce the tetrahydro derivatives in separate syntheses and isolate them, so that they can be used directly in the AO process. It is also known from U.S. Pat. No. 4,514,376 that the proportion of tetrahydro derivatives relative to the alkylanthraquinones in the working solution of the AO process can be increased by adding a solution produced separately by hydrogenation (palladium, 50 to 400 kPa, temperature not greater than 50.degree. C.) having an increased tetrahydro derivative content to a standard alkylanthraquinone working solution maximally in such an amount that the solubility of the tetrahydro derivative in the hydrogenation stage of the AO cyclic process is not exceeded. Although the foregoing process enables the production of hydrogen peroxide using working solutions with an improved ratio of alkyltetrahydroanthraquinone to alkylanthraquinone, it has not yet proved possible in the art to produce by a simple direct process working solutions which contain substantially only alkyltetrahydroanthraquinones as reaction carriers for producing hydrogen peroxide by the AO process.